I've been offered a place on an MA in University of Limerick in the above course. I was wondering if this MA would qualify me to teach in primary schools in the USA where I'm a citizen, or would I have to get additional certification in the States. I would appreciate any advice you have to offer, or who I could contact to get more information on this topic.

You'd need to check with the DOE in the specific state in which you'd like to teach.

Your best bet would be to try and do a full PhD in the UK. Then when you return to the US most states have a program that will allow you to teach for up to two years with no certification but with a relevant degree. You have to participate in their alternative certification program during that time which gives you either an add-on teacher cert or an M.Ed. The states will usually pay for this and it is done part-time so that's pretty nice.

But seriously, keep in mind if you ever plan to teach anywhere in the US (especially at the college level) that they won't accept a British MA in most cases so you'd need to complete the full doctorate degree.

It's because of the differences in length and specialization. US versus UK in the US primary school is 13 years, in the UK 11. The UK then adds on A-levels (or O-levels) which are like the 11th & 12th Grades in the US. The UK university degrees then are usually 2.5-3 years more. This only equates to an Associates degree in the US (sometimes a little more). The UK honors degrees sometimes equate to the US BA but not always. The UK masters programs tend to only be 1-1.5 years whereas most US programs are 2 years +.

So although there is nothing inherently better or worse about either system, they don't line up until the doctorate level. I've talked with LOTS of people who had masters degrees from UK universities and who had actually been teaching at the primary or college level in the UK who then were told by US or Canadian employers that they would have to go back to school and get an additional Masters to be employable.